Method of and apparatus for calibrating electric instruments



INVENTOR Harry P Sparkas;

ATIFORNEY H. P. SPARKES Original Filed Sept. 16, 1926 Dec. 20, 1932.

METHOD OF AND APPARATUS FOR CALIBRATING ELECTRIC INSTRUMENTS a a NU 0 \23. an.

Patented Dec. 20, 1932 for indicating directly any error which mayUNITED STATES.

my r. sranxns, or waste 'omnqn, NEW JERSEY, assreiron r0 wnsrmenonsnPATENT OFFICE ELECTRIC & MANUFACTURING COMPANY, A CORPORATIQN OFPENNSYLVANIA METHOD OF AND APPARATUS FOR CALIBBATING ELECTRICINSTRUMENTS Original application filed September 16,1926, Serial No.135,98l. Divided and this application filed April 27, 1929. Serial No.358,619. Renewed May 27, 18 32.

My invention relates to a method of, and

apparatus for, calibrating electrical integratin meters.

My invention is disclosed in my copendmg applicationfor Letters Patent,Serial No.

135,981, filed September 16, 1926, for improvement in method andapparatusfor calirating electrical instruments, of which the presentapplication is a division.

An object of my invention is to provide a method of calibrating watthourmeters which shall be adapted for use either in the factory or after themeters have been. in stalled on a customers premises.

A further object of my invention is to provide calibrating apparatusembodying means exist in the instrument being calibrated. For example,the indicating means embodying my invention may be calibrated to showany percentage error which may exist in the registration of theinstrument being tested. These and other advantages of my invention willappear more clearly from a consideration of the following detaileddescription of apparatus embodying the invention.

In accordance with my invention, the rotatable element of an integratingmeter to be tested is provided with equally spaced marks or indicia forcooperation with my stroboscopic device. Preferably, the edge of thedisc armature of the meter is employed for this purpose because thisedge is visible through the cover of the instrument and, consequently,permits the calibration of the instrument without removing the coverthereof. Lines may be painted on the edge of the disc or the edge of thedisc may be scored or ruled in a milling machine or ruling engine.

If lines are painted on the disc, the lines should'preferably be of acolor which is materially different from the color of the armature disc,although any color may be employed in connection with a color filter inthe optical system to be described.

The stroboscopic calibrating apparatus comprises a light sourcecontrolled in accord-.

ance with the correct speed of rotation of the integrating instrument insuch manner that the lines or indicia on. the armature member willappear stationary at some predetermined speed. For example, amotor-driven comsometimes desirable to determine the degree 08.

of accuracy of the instruments before correctmg the adjustment thereof.

In accordance with the present invention,

the last mentioned result is accomplished by the provision of anindicating device which 10 indicates the degree of accuracy of theinstrument being tested when the speed of the stroboscopic device hasbeen adjusted to correspond to the speed of the watthour meter.

The indicating device preferably comprises a watt-meter elementconnected in circuit relation with the watthour meter to be tested andmechanically coupled to a volt-meter element electrically associatedwith the stroboscopic device.

' The single figure of the accompanying drawing is a diagrammatic viewof a calibrating apparatus for a watthour meter vconstructed inaccordance with my invention, which figure corresponds to Fig. 2 ofsheet 2 of the application of which the present application is adivision.

Referring to the drawing, the calibrating apparatus illustrated isadapted for use in the factory-testing of a large number of instrumentswhich must be calibrated properly before being sold, or to determine thedegree of accuracy of theinstruments before correcting the adjustmentthereof after they have been installed in service. s

A watthour meter 1 is connected to a supply circuit 2, a load 3 beingconnected to the circuit 2 through the windings of the watthour 'meter 1winding 36 of the indicating instrument and the windings of a regulating100 device 4- associated therewith. Stroboscopic calibrating apparatus 5is also associated with the watthour meter 1 and is controlled by theregulator 4.

The watthour meter 1 comprises an electromagnet 8, an armature member 9controlled thereby and a register 10 driven by the armature member 9.The edge of the armature member 9 has evenly spaced marks or indiciathereon which are visible through a Window 11 in the cover member 12 ofthe instrument.

The regulator 4 comprises a Kelvin-balance type Watt-meter 15 in seriesrelation to the watthour meter 1, a dArsonval voltmeter 16 mechanicallyconnected to the movable arm of the Kelvin balance 15 and a variableresistor 17 controlled by pilot motor 18 in accordance with the relativetorques on the instruments 15 and 16.

The stroboscopic device's) comprises'a driving motor 21, a tachometergenerator 23 and a commutator 30, all disposed on thelshaft of the motor21, the commutator being adapted to interrupt thecurrent to a lightsource 22 in accordance with the speed ofrotation of the motor- 21.

In order to take care of the rapid interruptions in current through it,the light source 22 is preferably a lamp having an incandescent filamentof such character that it is heated and cooled rapidly as the current{herethrough varies, such as a neon gas-filled amp.

The driving motor 21 of the stroboscopic device 5 is connected, throughthe variable resistor 17 of the regulator 4, to the circuit 2. Theterminals of the tachometer generator 23 are'connected to the terminalsof the volt-meter 16, a calibrating resistor 28 being provided in thiscircuit.

The armature member 9 of the watthour N meter 1 rotates at aperdetermined speed, de-

pending upon the adjustment of the meter and the magnitude of the load3. If the adjustment of the meter is correct, its speed corresponds tothe speed of the stroboscopic device 5 so that the marks on the armaturedisc 9 of the watthour meter appear to an observer to remain stationary.This is the wellknown stroboscopic effect, and it is believed that theoperation will be clear without a detailed explanation of thephenomenon.

If the adjustment of the watthour meter 1 is incorrect, the armaturedoes not appear stationary, and the instrument is adjusted until thedesired speed of rotation is obtained: If a large number of equi-distantmarks on. the armature member 9 be employed, the instrument may beeasily and quickly adjusted with a high degree of accuracy. A

Ordinarily, variations in the potential of the supply circuit 2 aresufiicient to disturb the testing operation when a special source ofconstant potential is not used, and, conpensate for these variations.

sequently, the regulator 4 is provided to comof the circuit shouldincrease,'the load 3 would consume more energy and the instruments 1 and5 would both haveincreased torque. If the increase in voltage of the Ifthe voltage v supply circuit 2 does notincrease the speed of the drivingmotor 21 at the same rate as, the speed of the watthour meter 1, theKelvin tion, direct indication is obtained of the degree of accuracy ofthe watt-meter on the test. For example, the watt-meter 1 may be onethat has been installed upon a customers premises for a considerableperiod and it may be desirable to check its accuracy before an attemptis made to correct the adjustment of the meter.

- In this embodiment, while the commutator 30 is used to interrupt thecurrent to the lamp 22, it will be apparentto those skilled in the artthat this arrangement is equivalent to the light shutter shown in Fig. 1of the parent application.

A manually. adjustable resistor 31 is provided in the circuit of thedriving motor 21, and a change-over switch 32 is also provided to permitthe driving motor to be controlled either by the regulator resistor 17or the last mentioned'resistor 31. In some cases, theregulatingapparatus 4 may be omitted, and the regulation of the drivingmotor 21 accomplished solely by means of the adjustable resistor 31.

An indicating device 35' is so connected to the watthour meter '1 and tothe tachometer 23 as to indicate directly the degree of accuracy of thewatt-hour meter when the stroboscopic apparatus has been adjusted tocorrespondto the registration of the watthour meter 1.

The indicating device 35 comprisesa wattmeter' 36 of the,electro-dynamic type, mechanically coupled to a volt-meter 37 of thedArsonval type. The watt-meter 36 is so connected in series with thewatthour meter 1 thatit will be energized in accordance with themagnitude of the load 3 connected to the watthour meter 1. Thevolt-meter 37 is so connected to the tachometer generator 23 that it isenergized in accordance with the speed of rotation ofthe driving motor21 of the stroboscopic apparatus. The driving motor 21 is adjustedbymeans of the variable resistor 31 until the speed of the stroboscopicinstalled on customers premises.

a paratus corresponds to the registration of t ewatthour meter 1. If thewatthour meter 1 is in correct adjustment, the torque of the watt-meter36 exactly balances the tor ue of the volt-meter 37, and the pointer oft e indicating device 35 indicates the accuracy of the instrument undertest to be If the watthour meter 1 has an error, the necessaryadjustmentofthe stroboscopic apparatus 5 alters the speed of the tachometer 23,and the volt-meter 37 has a greater or less torque than that of thewatt-meter 36. Consequently, the pointer of the indicating device 35indicates that the watt-hour meter 1 has a positive or a negative error.The scale of the indicating device 35 is preferably calibrated toindicate the percentage error, as indicated.

The apparatus heretofore described is preferably disposed in a portablecarrying case to facilitate the testing of the instruments In such case,the automatic regulating apparatus 4 may be omitted, and the speed ofthe driving motor 21 of thestroboscopic apparatus be controlled by theresistor 31. In accordance with the provisions of the patent statutes, Ihave described the principle of operation of my invention, together withapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown anddescribed is only illustrative and that the invention may be practicedby other means.

I claim as my invention:

1. Calibrating apparatus for integrating instruments comprisingstroboscopic means for checking the speed of rotation of the instrumentupon a predetermined load, an indicating device comprising a wattmeterelement and a second element mechanically coupled together andconnections between the elements of said device and the circuits of theintegrating instrument and the stroboscopic means, whereby the deviceindicates the degree of accuracy of the instrument.

2. Calibrating apparatus for integrating instruments comprisingstroboscopic means for checking the speed of rotation of the instrumentupon a predetermined load, an indicating device comprising a wattmeterelement and a second element mechanically'coupled together andconnections between the elements of said device and the circuits of theintegrating instrument and the strobescopic means, whereby the deviceindicates the degree of accuracy of the instrument and speed-regulatingmeans for the stroboscopic means to compensate for variations in thesupply-circuit potential.

3. The method of calibrating electrical instruments of the integratingtype which consists in comparing the speed of rotation of theintegrating instrument with the rapidity of movement of a second device,regulatin the movement of the latter in accordance wit varlations in thepotential applied to the in strument and balancing the torqueproportional to the load on the instrument and the rapidity of movementof the second device, res ectively, in order'to obtain a-directindication of the degree of accuracy of the instrument being tested.

4. In combination, a watthour meter to be calibrated having a rotatableelement, means for imposing a load on said watthour meter, a standard ofcomparison embodying a rotatable element, means forad'jus in-g thestandard so that the speed of rotation of its rotatable element bears adefinite ratio to.the speed for comparing the relative speeds ofrotationi of the rotatable elements, and indicating" means actuated inaccordance with the speed of the standard element and-the load on thewatt-hour meter to indicate the error of the latter.

5. In combination, a watthour meter to be calibrated having a rotatableelement with evenly spaced marks thereon, means for applying. testloadsto said meter, a lamp for illuminating, the evenly spaced marks,adjustable means for intermittently energizing the lamp at such a ratethat said marks appear stationary, and means actuated in accordance withthe load imposed on the meter and the frequency at whlch energizingimpulses arenappliedto the lamp for indicatin in terms of per centregistration the error 0 the meter.

6. In combination, a plurality of electrically operated devices eachcomprising a' movable member, a common source of power for said devices,means for varying the speed of one movable member, means for indicatingcoincidence in the speeds of said movable members, and means controlledby said first named means for giving a direct indication of variance inthe speeds of the movable members. 1

7. In combination, a plurality of electrically operated devices feachcomprising a movable member, a common source of power for said devices,means for varying the speed of one movable member, stroboscopic meansfor indicating coincidence in'the speeds of said movable members, andmeans controlled by said first named means for giving a directindication of variance in the speeds of themovable members.

8. In combination, a plurality of elements movable in response to acommon influence, means for varying the movement of one of saidelements, and means responsive to oper- 9. In combination, aplurality ofelements capable of different movements in response to a commoninfluence, one of said elements operating as a standard to move at'agiven rate in response to .a given influence, and means for varying therate of the standard element to agree with the movement of another ofsaid elements in response to a given influence, and means responsive tooperation 13 of said varying means for giving a direct indication of thedeparture of movement of said other element from the movement. of thestandard element.

10. In combination, a pair of electrically l operated rotatable devicesand means for causing the rotation thereof, means for stroboscopicallycomparing the speeds of said devices, means for varying the speed ofrotation of one of said devices, and means 0 controlled by said var ingmeans for giving a direct indication o the amount of variance in thespeeds of said devices.

11. In combination, a pair of rotatable de-. vices and means for causingthe rotation thereof, means for stroboscopically comparing the speeds ofsaid devices, means for varying the speed of rotation of one of saiddevices, and means controlled by said varying means for giving a directindication of the amount of variance in the speeds of said:

devices.

In testimony whereof, I have hereunto iglgigcribed my name this 18th dayof April,

'35 HARRY P. S'PARKES.

